A portion of the grpah of the polar function = f(delta), where
f(delta)=3 cos(3delta), is shown in the polar coordinate system for a≤ delta ≤b.
If 0≤a a and b?
(A) a=0 and b=pi/6
(C) a=pi/3 and b=pi/2
(B) a=pi/6 and b=pi/3
(D) a=5pi/4 and b=3pi/2